Preclinical Experimental Study Of Fully Bioabsorbable Vascular Scaffolds

Part ?Improved Hydrophilicity of Nano-Amorphous Calcium Phosphate Encourages Poly-L-Lactic Acid Application in Vascular ScaffoldsBackground:Abbott's BVS Scaffold has brought new thinking to the development of biodegradable scaffolds due to it's delisting events.A single PLLA material does not fully meet the needs of a biodegradable stent.One of the main reasons is that the PLLA material is a hydrophobic material with poor cell compatibility,which is an important cause of late stent thrombosis.Objective:To address the hydrophobicity and cytocompatibility of PLLA material scaffolds.This study adds biodegradable nanoscale ACP materials to the PLLA material.This study further evaluated whether the hydrophobic properties and cell and blood compatibility of PLLA/ACP nanobioabsorbable scaffolds were significantly improved.Methods:This value was tested by a hanging drop method using a contact angle analyzer to determine the static contact angle of the different materials to evaluate the wettability of the polymer surface.The hemolysis rate was measured by immersing different materials in diluted rabbit acid-citrate-glucose blood for 60 minutes.Platelet adhesion test Different groups of material membranes were exposed to platelet-rich plasma,washed with double distilled water,and examined by scanning electron microscopy for substrate platelet aggregation.The PLLA and PLLA/ACP membranes were each placed in a 24-well plate,incubated with whole rabbit blood,and the P-selectin kit was tested to detect P-selectin levels to assess platelet activation.The cytotoxicity of different materials was examined by co-culture of ECV304 cells with different polymer membranes.The inflammatory response was assessed using different polymer membrane pain THP-1 cell co-culture ELISA kits(concentration of pro-inflammatory cytokines(IL-6 and TNF-?)in culture supernatants.Seven PLLA scaffold tubes and seven PLLA/ACP scaffold tubes were implanted into the radial artery of 14 rabbits.After 6 weeks,the animals were sacrificed for blood biochemistry and histopathology.Results:Hydrophilicity was investigated by calculating the static contact angle of ultrapure water,which confirms that the static contact angle of PLLA/ACP is significantly smaller than the static contact angle of PLLA(78.50±1.90 vs.89.10±1.30,P<0.01).Both polymers have good hemolysis properties in the hemolysis test(PLLA/ACP vs.PLLA:1.7%vs.2.1%).In the platelet adhesion test,less activated platelets were found than the PLLA/ACP membrane compared to the PLLA membrane(0.52±0.08 vs.1.0±0.21,P<0.05).According to microscopic observation,cell compatibility studies indicated that more cellular multiples occurred,forming a confluent ECV304 cell layer,and the pseudopods of the cells extended and thus developed more fully on the PLLA/ACP membrane than on the PLLA membrane.In addition,the ELISA results showed PLLA/ACP caused lower release of IL-6 and TNF-? than PLLA group(10.3±1.4 vs.30.0±3.7 vs.247.4±26.6;P<0.01)(11.8±2.6 vs.35.0±2.8,P<0.01).No systemic biochemical toxicity of PLLA or PLLA/ACP was found in the rabbit radial artery stent model.Conclusion:PLLA polymers mixed with ACP nanoparticles exhibit significantly increased hydrophilicity,less platelet adhesion and lower platelet activation,more fully developed ECV304 cell margins and reduced PLLA groups in vitro and in vivo The inflammatory response has very good hemolysis properties,and co-formulation of ACP with PLLA improves its blood compatibility and cytocompatibility.PLLA/ACP is a better material ratio choice for future clinical applications of bioabsorbable scaffold platforms.Part ?Long-term Inflammatory Response of Vascular Tissue after Implantation of Babsorbable PLLA/ACP Scaffold into Porcine Coronary ArteryBackground:After the high molecular polymer PLLA scaffold is implanted into the blood vessel,the acidic metabolite lactic acid will be produced during the degradation process,which will cause long-term chronic inflammatory reaction to the surrounding tissue,which may lead to the risk of intimal,smooth muscle hyperplasia and in-stent restenosis.Therefore,in view of the shortage of PLLA materials,our group added nano-scale ACP materials capable of generating basic groups after degrading in PLLA,and the two materials were blended to form a novel bioabsorbable PLLA/ACP scaffold.Objective:In this study,through the improvement of the biodegradable PLLA scaffold material,it is observed whether the composite PLLA/ACP scaffold after increasing the nano-scale ACP material can alleviate the inflammatory reaction to peripheral vascular tissue during the degradation of PLLA material scaffold,and the mechanism is discussed.Methods:Twenty-four PLLA stents and 24 PLLA/ACP stents were implanted into the porcine coronary arteries,and each of the minipigs was implanted with two identical scaffolds.Arterial serum was taken before operation,1 month,6 months,12 months,and 24 months after surgery to determine the contents of ALT,AST,UR,Cr,LDH and CRP.The pathological morphology of the stent was taken out,the inflammation score and fibrosis score were detected by HE staining,and the positive expression index of MMP-9 and NF-?B was detected by immunohistochemical staining.Western Blot was used to detect the expression of inflammation-related proteins IL-1 and IL-6.Results:Hematology results showed that the two groups of stents did not cause significant changes in blood ALT,AST,UR,Cr,LDH,CRP,and there was no statistically significant difference between PLLA group and PLLA/ACP group(P<0.05).The inflammation scores in the PLLA/ACP group were lower than those in the PLLA group at 6 months,12 months,and 24 months after surgery(P<0.05).The PLLA/ACP group fibrosis scores were lower than those in the PLLA group at 12 months and 24 months after surgery(P<0.05).The results of immunohistochemistry showed that the expression indexes of MMP-9 and NF-?B in PLLA/ACP group were significantly smaller than those in PLLA group at 6 months,12 months and 24 months(P<0.05).Western Blot results showed that IL-1 protein expression in PLLA/ACP group was significantly lower than that in PLLA group at 12 months and 24 months after surgery(P<0.01).The expression of IL-1 protein was significantly lower in the PLLA group(P<0.01)at 6 months,12 months,and 24 months after surgery.Conclusions:The inflammatory response of PLLA scaffolds is prolonged with the prolonged implantation time,and the inflammatory response of vascular tissue around the scaffold is gradually aggravated.The integration of low-dose nano-level ACP can alleviate the long-term chronic inflammatory response after PLLA scaffold material implantation.Nanobioabsorbable PLLA/ACP scaffold materials have good biosafety and histocompatibility with mild inflammatory response.Therefore,the application prospect of the nano-bioabsorbable PLLA/ACP scaffold is more optimistic,which can broaden the new ideas for the development of nano-bioabsorbable vascular scaffold in the future.Part ?Six Months Observation of Bioresorbable PLLA/ACP Scaffold Implanted into Porcine Coronary ArteryBackground:The inability of the metal stent to degrade brings about an active late vascular recovery problem.Biodegradable scaffolds bring new ideas,but the current use of PLLA material scaffolds has limited biocompatibility and mechanical support properties and vascular performance needs to be further improved.The nanobioabsorbable PLLA/ACP scaffold used by our group can meet the design requirements and have good biological and mechanical properties.Objective:Coronary angiography QCA and intravascular ultrasound IVUS were used to evaluate the effectiveness of a new fully bioabsorbable stent consisting of PLLA/ACP and its performance at 6 months follow-up of the coronary arteries by comparison with the PLLA stent.MethodsTwelve PLLA/ACP stents and 12 PLLA stents were implanted into the coronary arteries of 12 minipigs(two scaffolds per minipig).Quantitative coronary angiography(QCA)was used to measure reference vessel diameter(RVD),mean lumen diameter(MLD),and late lumen loss(LLL).Based on the IVUS image,we calculated post-implantation stent rod malapposition rate(SMR),stent rod overlap rate(SOR),reference vessel area(RVA),mean stent area(MSA),mean lumen area(MLA),and tube Cavity patency rate(LPR).ResultsThe QCA results showed that at 6 months,the MLD of the PLLA/ACP stent was larger than the PLLA stent(2.47 ± 0.22 mm vs.2.08±0.25 mm,P<0.05);the LLL of the PLLA/ACP stent was smaller than the LLL of the PLLA stent(0.42 ±0.20 mm vs.0.75 ± 0.22 mm,P<0.05).The IVUS results showed that the SMR and SOR of the PLLA/ACP stent were significantly lower than the PLLA stent(5.84%±3.56%vs.17.72%± 4.86%,P<0.05)(6.17%±4.63%vs.17.65%± 4.29%,P<0.05).MSA,MLA and LPR of PLLA/ACP scaffolds were larger than PLLA scaffolds(6.35±0.45 mm2 vs.5.35±0.51 mm2,P<0.05),(4.76±0.46 mm2 vs.3.77±0.46 mm2,P<0.05),(78.01%±12.29%vs.61.69%±9.76%,P<0.05).ConclusionThe PLLA/ACP scaffold system has better release effect,and the stent has smaller elastic retraction and better adherence.Compared with the simple PLLA scaffold,the PLLA/ACP scaffold is implanted into the small pig coronary artery for 6 months.High,less lumen loss;and the PLLA/ACP scaffold implanted in the mini-porcine coronary artery maintains the stent shape for 6 months,and the support performance for the blood vessel is better than that of the pure PLLA scaffold.